The enthusiasm for nuclear power in the United States peaked in the late 1960s and early 1970s (if you graph it out, there is a peak in 1968, then a crash, then another, smaller peak in 1974), but even at that point it was considered a "niche" form of power generation. The companies that built these plants did them as something new to round out their energy portfolios with, not as a major piece of their business. The extremely high capital costs for nuclear power plants meant that you had to make a rather large gamble that they would be able to function economically for the next several decades, and that they would remain profitable compared to other forms of electrical generation — not easy things to predict.

So what one finds if one looks at the data is that all orders for new nuclear plants had crashed to zero by 1978, before Three Mile Island. This was just about economics.

Once Three Mile Island happened, it intensely complicated the situation for nuclear power. There were still plants that were under construction (they had been ordered before the accident), and the fears of accidents increased the number of lawsuits and challenges to their development. This spread out their construction time immensely; the Seabrook plant had its construction permit granted in 1976, for example, but was not completed until 1986, and not online until 1990, and even then it was only constructed to half of its original capacity (one unit, not two). This is an extreme example but exemplifies the financial risk involved — this is not the sort of thing you want to tie up a few billion dollars up with. The Three Mile Island station cost $400 million to construct at the time, equivalent to about $2 billion dollars today — this is what we mean by it being capital intensive!

The accident at Three Mile Island made the regulatory landscape much more stringent, and also increased the opposition. It generally soured private company's perspective on nuclear power — why would they invest in nuclear when they could throw up a dozen coal and natural gas plants at a fraction of the cost and time? Even insulated from the insurance problem of accidents (the Price-Anderson Act of 1957 indemnifies them from accident costs), it was still a lot of risk to take on for a power source that ultimately would take decades to potentially turn profit, and would require them to cede a lot of authority to others in the world (the federal government, the global uranium suppliers, etc.).

Chernobyl just heightened the trends already in place. There were no new orders for nuclear plants filed in the USA until the 21st century, and we'll see how many of those actually get built, in the end.

Pro-nuclear activists in the USA tend to blame NIMBYs for the fall of nuclear power here, but that's only part of the story. The real problem from the beginning was economics. Nuclear power is not ideal for the private sector, not without a lot of incentives and guarantees secured from elsewhere (like the government). In the USA, that has been a huge problem because the people who support nuclear power tend to also support a free-market approach to it. But the free market doesn't readily support nuclear power, in the end, at least not on the terms that are allowable by regulatory agencies. One could imagine nuclear power today being heavily subsidized or even developed as a government service — and I usually suggest that those who think we must go to carbon-neutral power output should start thinking along these lines. But I think it is just convenient to blame it on environmental activists, NIMBYs, and hippies, because it makes it a question of trying to convince (or exclude) people, which is easier to tackle than the economics of the thing.

Interestingly, these economic issues exist in non-capitalist societies as well (because even if they don't need to turn a profit, they need to justify the resource expenditure), and are part of the reason why the Soviets chose the ill-fated RBMK nuclear reactor in the first place (it was more economical in the Soviet context than their pressurized water designs).

Anyway, the best overall book on the US nuclear reactor history, and the role of Three Mile Island as a catalyst to problems already existing, is J. Samuel Walker's Three Mile Island. It's a good read. Walker was the former official historian of the Nuclear Regulatory Commission and takes a very even-handed approach to the whole issue.